Raman spectra of vacancy-containing LiF: Predictions from first principles

Sorokin, A.V.; Piskunov, Sergei; Isakoviča, Inta; Makarenko, I.; Karbovnyk, Ivan; Попов, А. И.

doi:10.1016/j.nimb.2020.07.025

Cited by 8 publications

(6 citation statements)

References 57 publications

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“…One of the most distinctive features is located at 519 cm -1 and may correspond to the Sm atoms vibrating around a quasi-stationary N atom. This feature is likely to be only affected by the nearest neighbouring atoms to the nitrogen vacancies, similar to what is seen in LiF [124]. Such a scenario aligns well with the decrease of the signal intensity for lower VN levels (higher RN2/Sm).…”

Section: Raman Spectroscopysupporting

confidence: 77%

Effect of the Growth Conditions on the Properties of Rare Earth Nitride Thin Films

Shaib¹

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The members of the rare earth nitride (REN) series are intrinsic ferromagnetic semiconductors that bring together attractive electronic and magnetic properties for fundamental investigations and spintronics applications. So far, most of the research on rare earth nitrides is focused on their electrical transport and magnetic properties, leaving a significant knowledge gap to determine and understand the effect of growth conditions on their structural properties. In this thesis, we propose a study on the effects of the growth conditions, with an emphasis on the influence of the ratio of N2 to RE (RN2/Gd) during the growth, on the structural, electrical transport, magnetic, and optical properties of a series of REN thin films. We begin by investigating the effects of RN2/Gd during the catalytic growth of polycrystalline GdN thin films of their structural, electrical transport, magnetic, and optical properties. Electrical resistivity of the films increases by four orders-of-magnitude for a less than two orders increase of RN2/Gd. Hall resistivity measurements indicate a parallel decrease in the carrier concentration, suggesting decreased nitrogen vacancy (VN) levels in the films for higher RN2/Gd. 2θ-θ X-ray measurements indicate arising asymmetry in the dominant GdN 111 peak at higher VN concentrations, suggesting the presence of a second structural phase of GdN (GdN-II) of a smaller lattice constant that is associated with N-deficient regions of the films, alongside a stoichiometric phase (GdN-I). Magnetic data indicate enhanced Curie temperature at higher VN levels, possibly due to the formation of magnetic polarons at VN sites, and the coercive field data at low temperature suggests a soft ferromagnetic nature of GdN-II. Raman spectroscopy does not point to a clear link between the weak Raman signal observed in the RENs and the level of VN in the films. We next explore the preferential growth nature of SmN and the effect of RN2/RE on the structural, electric transport, magnetic, and optical properties of polycrystalline SmN and DyN thin films. XRD diffractograms indicate SmN exhibits a competitive growth following an evolutionary model and grows preferentially along the (111)-crystal orientation. Both SmN and DyN experience a stark increase in film resistivity for a small increase in RN2/RE, and Hall effect measurements on SmN suggest high VN concentration in the most conductive films (~9%). Although both SmN and DyN experience lattice constant reduction at higher VN content, neither show evidence for a second structural phase. The Raman signal in SmN films is also weak; however, the broadness of the RN2/RE range used during film growth allows identifying strengthening of the Raman signal when more vacancies are present. The origin of the signal is still uncertain, yet 2nd order distortions such as tetragonal distortions associated with VN could likely be the culprit. Magnetic measurements on DyN show enhancement of TC for lower RN2/Dy in a similar fashion to GdN. DyN’s magnetic moment nears Hund’s rule moment in films with high VN, possibly indicating a role played by VN in suppressing the crystal field quenching effects. Lastly, we report on growing epitaxial films of Gd and Sm on AlN templates that we nitride via flooding the growth chamber with pure N2 gas, and RHEED is used to monitor the real-time lattice evolution. The Gd thin film displays rapid incorporation of nitrogen at ambient temperature, yet experiences delay at high temperature. XRD diffractograms show evidence of a broad peak corresponding to GdN with a shrunk lattice constant, while magnetic data suggest the nitrided layer is not what to expect from a traditional diffusion model, but instead is formed of two separate layers of GdN and Gd. We carried a cycle of Sm growth followed by nitridation/denitridation, while increasing the nitrogen pressure with each new stack. RHEED patterns display lattice spacing corresponding to both divalent and trivalent Sm, in contrast with previous reports. Incorporation of nitrogen is fast for all cycles, and a SmN RHEED pattern corresponding to VN-rich SmN is produced. Although the first cycle of denitridation results in no change to the RHEED pattern, subsequent cycles achieve complete reversal of the pattern back into a pattern resembling Sm metal. This is of great importance for applications requiring the presence of atomic nitrogen like the production of ammonia.

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Section: Raman Spectroscopysupporting

confidence: 77%

Effect of the Growth Conditions on the Properties of Rare Earth Nitride Thin Films

Shaib¹

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“…), which requires additional dedicated work. Recently, similar work was conducted, for example, for SrTiO3 crystal with oxygen vacancies [59,60].…”

Section: Luminescence Spectra Of Sintered and Commercial β-Ga 2 O 3 C...mentioning

confidence: 99%

“…), which requires additional dedicated work. Recently, similar work was conducted, for example, for SrTiO 3 crystal with oxygen vacancies [59,60]. Why annealing of Ga 2 O 3 ceramics can greatly change the concentration of vacancies, as well as their transformation into more complex ones, is not such a difficult question.…”

Section: Luminescence Spectra Of Sintered and Commercial β-Ga 2 O 3 C...mentioning

confidence: 99%

Study of β-Ga2O3 Ceramics Synthesized under Powerful Electron Beam

Usseinov,

Karipbayev,

Purans

et al. 2023

Materials

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The synthesis of β-Ga2O3 ceramic was achieved using high-energy electron beams for the first time. The irradiation of gallium oxide powder in a copper crucible using a 1.4 MeV electron beam resulted in a monolithic ceramic structure, eliminating powder particles and imperfections. The synthesized β-Ga2O3 ceramic exhibited a close-to-ideal composition of O/Ga in a 3:2 ratio. X-ray diffraction analysis confirmed a monoclinic structure (space group C2/m) that matched the reference diagram before and after annealing. Photoluminescence spectra revealed multiple luminescence peaks at blue (~2.7 eV) and UV (3.3, 3.4, 3.8 eV) wavelengths for the synthesized ceramic and commercial crystals. Raman spectroscopy confirmed the bonding modes in the synthesized ceramic. The electron beam-assisted method offers a rapid and cost-effective approach for β-Ga2O3 ceramic production without requiring additional equipment or complex manipulations. This method holds promise for fabricating refractory ceramics with high melting points, both doped and undoped.

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“…Voit et al [81] Toth et al [82] Dracopulos et al [17] vibrational frequency), it can be inferred that the existence of these bands are the result of presence of defects in the structure, [79] which causes the degeneracy to break. Based on the results shown in Figure S1, the closest agreement with experiment is for the PBEsol-D3.…”

Section: Zrf 4 -Lif Systemmentioning

confidence: 99%

“…[75] In another study, the phonon density of states of LiF calculated at PBE level generated a maximum of 450 cm À1 frequency. [76] Ultimately, reviewing the aforementioned studies of Sorokin, Evans, and Heilmann, [77][78][79] it is inferred that experimental Raman spectrum of LiF should have bands at 88, 142, 168, 330, 416, 450, 476, 543, 611, and 655 cm À1 . For the experimental infrared spectra of LiF, there exists only one sharp band around 313 cm À1 and two weak bands at 485 and 650 cm À1 , which appear to be sensitive to temperature.…”

Section: Zrf 4 -Lif Systemmentioning

confidence: 99%

Effect of XC functionals and dispersion corrections on the DFT‐computed structural and vibrational properties of SrCl₂–NaCl and ZrF₄–LiF

Mofrad,

Christian,

Schorne‐Pinto

et al. 2024

J Raman Spectroscopy

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Density functional theory (DFT) calculations were performed to examine the impact of exchange–correlation (XC) functionals and van der Waals corrections (specifically the D3 method) on the structural and vibrational properties of the SrCl2–NaCl and ZrF4–LiF salt systems. Multiple XC functionals, including the local density approximation (LDA), the generalized gradient approximation using the Perdew–Burke–Ernzerhof (PBE) model, and its modified form suitable for solids (PBEsol), the dispersion‐corrected PBE‐D3 and PBEsol‐D3, were considered. Of these functionals, LDA was found to exhibit the highest degree of error, while PBEsol and PBE‐D3 displayed the least error. Underestimated lattice parameters compared with experimental values were observed to result in higher force constants, leading to an overprediction of vibrational frequencies. Conversely, an overestimation of lattice parameters was associated with lower vibrational frequencies. The methodology presented in this study yielded results that are in good agreement with experiment, irrespective of the method (finite differences vs. density functional perturbation theory) employed for calculating infrared and Raman spectra. It was further demonstrated that for alkali halides with weak Raman scattering, utilizing a supercell constructed from primitive cells better predicts Raman features than does the use of conventional cells.

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Raman spectra of vacancy-containing LiF: Predictions from first principles

Cited by 8 publications

References 57 publications

Effect of the Growth Conditions on the Properties of Rare Earth Nitride Thin Films

Effect of the Growth Conditions on the Properties of Rare Earth Nitride Thin Films

Study of β-Ga2O3 Ceramics Synthesized under Powerful Electron Beam

Effect of XC functionals and dispersion corrections on the DFT‐computed structural and vibrational properties of SrCl₂–NaCl and ZrF₄–LiF

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Raman spectra of vacancy-containing LiF: Predictions from first principles

Cited by 8 publications

References 57 publications

Effect of the Growth Conditions on the Properties of Rare Earth Nitride Thin Films

Effect of the Growth Conditions on the Properties of Rare Earth Nitride Thin Films

Study of β-Ga2O3 Ceramics Synthesized under Powerful Electron Beam

Effect of XC functionals and dispersion corrections on the DFT‐computed structural and vibrational properties of SrCl2–NaCl and ZrF4–LiF

Contact Info

Product

Resources

About

Effect of XC functionals and dispersion corrections on the DFT‐computed structural and vibrational properties of SrCl₂–NaCl and ZrF₄–LiF